General Background Art
Keyboards are essential input devices for many applications, including for personal computers. As described above, such personal computers are often designed to be transportable and have been occupying less cubic volume over time. An example of such a portable personal computer is described in coassigned U.S. Pat. No. 5,198,991, incorporated by reference herein for the purpose of describing the computer per se and the connections between the computer and a folding keyboard, and such description will not be repeated here.
The miniaturization of data processing equipment, for portability and ease of use, is becoming increasingly important. However, there are some factors which place practical limits on the miniaturization which could theoretically be achieved.
The limiting factor for reducing the size of portable data processing equipment is generally the keyboard. A keyboard requires sufficient size, in terms of horizontal dimensions, for the keys. Keys are constrained to at least a certain minimum size, because they must have a size and spacing commensurate with the size of an average operator's fingers and hands.
Keyboards also requires mechanics, for converting keystrokes to electrical signals representative of operation of the keys. Some minimum thickness must be provided for these components. Also, the keys preferably have enough vertical displacement to give the user a good tactile feel.
Some conventional keyboards, particularly full-size desktop computer keyboards, have used mechanics such as "chimneys," sleeves that slide up and down. Such structures provide the advantage that all parts of the key are stable pressing down. That is, the key is constrained to a single, vertical transnational degree of freedom, so the key presses down in a vertical fashion.
Another conventional structure that of using scissors that use two members that pivot at the center and are attached at one end and the other end of them slides a lot, one can achieve pressing anywhere on the key (pressing the key vertically up and down.
Prior U.S. Pat. No. 5,280,147, Mochizuki et al., assigned to Brother Kogyo Kabushiki Kaisha, reduces the thickness of the keyboard by the use of scissors-like pivotally connected support levers with pivot connections at one end of each lever to respectively the base and the key, and sliding pivot connections at the opposite ends. A conventional nonlinear rubber spring or "dome" is used to transmit the keystroke to electrical contacts to make the connection, indicating operation of the key.
These mechanisms are fine for desktop keyboards, when there is vertical space to be had. However, they are less suitable for portable computers. Such computers are designed for small size and light weight. In particular, reducing the thickness, and producing a "thin" keyboard, has been an important design objective. For such thin keyboards where there is little vertical space, other mechanisms have been used.
A typical portable data processor, or "portable personal computer" or "personal digital assistant", has a keyboard panel and a display panel, and the data processor is incorporated within one of the panels. The two panels are then folded together so that the bottom of the keyboard panel and the back of the display panel from an outer case for the folded unit. By reducing the thickness of the keyboard, the thickness of the overall folded unit may also be reduced, making the folded portable data processing unit easier to handle and to carry.
Prior U.S. Pat. No. 5,457,453, Chiu et al., unassigned, illustrates a keyboard having reduced thickness when folded, by moving otherwise conventional plunger keys to depressed positions when folding is to occur.
U.S. patent application Ser. No. 08/801,833
Co-pending, co-assigned U.S. patent application Ser. No. 08/801,833, now U.S. Pat. No. 5,874,697 Selker et al., "Thin Keyboard," describes keyswitches and a thin keyboard assembly. This co-pending patent application is hereby incorporated by reference. As background information for the present patent application, the apparatus described in the '833 application will be described here, in some detail. FIGS. 1, 2, 6, 7, and 8 of the '833 application are reproduced as FIGS. 1, 2, 3, 4, and 5, respectively, of the present patent application.
The assembly comprises a sheet member having a plurality of key faces fixed thereon in a conventional keyboard arrangement. A plurality of cutouts are made in the sheet member partially surrounding each key face. The cutouts define hinge members, which are cut away from the rest of the sheet member, typically on three of four sides, so that the hinge members have some freedom to flex, relative to the remainder of the sheet member. Key faces will be affixed to, or molded onto, the hinge members so that, when a user depresses the key face with a fingertip, the hinge member is subjected to a flexing force.
A plurality of living hinges (that is, hinges made from the same material making up the hinge members themselves, the hinges having greater resiliency and flexibility than the remainder of the hinge member, so that externally applied stress causes flexing of the living hinge, rather than flexing of the remainder of the hinge member) are made in the hinge members at one side of each key face.
Accordingly, the key face may be depressed, causing the key face to pivot about the living hinges to operate a corresponding set of electrical contacts, indicating operation of the key. A conventional rubber spring may transmit the pivot motion of the key face to the electrical contacts.
Two embodiments are given, one comprising a planar sheet with a single living hinge at one side of each key, whereby depression of the key face causes the key face to pivot downward about the living hinge. The other embodiment comprises two living hinges at one side of each key, allowing the key face to remain level while the pivoting about both hinges. Such a key requires advantageously low force to be operated.
Referring to FIG. 1, a keyboard assembly 10 is comprised of a plurality of key faces 11 arranged in rows according to the conventional "QWERTY" format. A face plate 12 covers the spaces of the keyboard assembly between the key faces. Electrical lines 14 and 15 extend from the keyboard assembly for connection to a data processor, as will be described. A base plate of the keyboard and the face plate 12 are connected together about the periphery of the keyboard as shown by edges 50 and 51.
The First Embodiment of the '833 Application
FIG. 2 illustrates, in greatly expanded scale, the first of the embodiments of the '833 application. A planar sheet 20 extends under the face plate 12 of the keyboard assembly of FIG. 1. The planar sheet preferably comprises a plastic material having both aspects of flexibility and of stiffness. The preferred material is Mylar.
One of the key faces 11 is affixed to, or molded onto, the planar sheet 20. Thus, the key faces 11 are supported by the planar sheet 20. A cutout 22, forming a hinge member, extends partially around the key face 11, on three sides thereof. Each end, or terminus, of the cutout 22 may be squared off, or, preferably, comprises a rounded terminus 23 and terminus 24.
The termini of the ends of the cutout are connected by a living hinge 26, forming a center section 28 of the planar sheet.
Thus, depression of the key face 11 causes the key face and center section 28 to pivot downward, rotating about the living hinge 26. The living hinge is a natural consequence of the positioning of the termini 23 and 24, but alternatively may be etched or cut into the planar sheet 20.
Unfortunately, the pressure required at one end of the key (at the top of the key) was much lower than at the bottom of the key where the hinge was made. The difference between 200 grams and 50 grams was measured. In fact, if one pressed very close to the hinge, one would imagine that there would be no motion at the hinge if one presses on the hinge itself.
The Second Embodiment of the '833 Application
FIGS. 3, 4 and 5 illustrate, in greatly expanded scale, a second embodiment of the invention described in the '833 application. This alternative sheet member and keyswitch arrangement required a substantially reduced actuation force. The actuation force for the keyswitch arrangement of FIG. 2 is approximately 80 grams, whereas the arrangement of FIGS. 3-5 is approximately 60 grams.
Referring to FIGS. 3-5, the sheet member 70 extends under the spacer 46 of the keyboard assembly of FIG. 1. The planar sheet 70 is the same material as planar sheet 20, preferably comprising a plastic material having both aspects of flexibility and of stiffness, such as Mylar. One of the key faces 11 is affixed to and supported by the planar sheet 70.
A cutout 72 extends partially around the key face 11, on three sides thereof, and forms a first living hinge 73. The cutout 72 continues inward, towards the center of the key 11 to form a terminus 75 and a terminus 76. The termini of the ends of the cutout are connected by a second living hinge 77, under the key face 11.
The cutout 72 thereby forms a center section 28 of the planar sheet, forming a hinge member. The hinge member includes a key face section, a center or intermediate section, and a base section, and two living hinges 73 and 77 at which the sections interface.
Thus, depression of the key face 11 causes the key face and center section 78 to stay level and pivot about the living hinges 73 and 77, moving forward slightly, to move from the quiescent, unactuated position of FIG. 4 to the depressed, actuated position of FIG. 5.
The living hinges 73 and 77 are a natural consequence of the positioning of the cutout 72 and the termini 75 and 76, but alternatively may be etched or cut into the planar sheet 70.
The mechanism of FIGS. 3-5 preferably is implemented as a mylar double hinge. By having the hinge off a piece of mylar be a line that bends, then a segment that does not bend, and another line that bends, followed by a piece of plastic on top to hold the key, the back of the key requires the same force to press down, even though it is close to the hinge.
It has been found that the mechanism of FIGS. 3-5 advantageously improves the evenness of required keystroke pressure. However, there is room for further improvements in key apparatus technology, so as to provide more even pressure requirements, while also being thin and lightweight enough for use with portable computers.